I haven't seen this problem caused by using track changes. I have seen it,
generally in Word 97 but also a bit in Word 2000, when there's one or more
corrupt tables in the document.
Try round-tripping to HTML (as a Web Page, *not* Web Page Filtered) or RTF
by using File > Save As.
And, you might like to investigate and similarly disinfect (a) the template
on which this document was created and (b) any other documents that were
created from the same template or created from this document. That is,
consider that there might also be problems in parent, sibling and descendent
documents. (I once had a problem in a template that caused every policy and
procedure in one department to exhibit this problem. They'd all inherited
the problem from the template.)
Hope this helps.
Shauna Kelly. Microsoft MVP.